In iontophoresis, the intensity of the acid and alkaline reactions at the poles depends on which of the following?

• A. The intensity of the current at each pole
• B. The relative density of the current at each pole
• C. Both A and B
• D. Neither A nor B

Answer: (C)

In iontophoresis, the chemical changes at the electrode surfaces (acid at the anode and alkali at the cathode) are driven by electrical current. The amount of these reactions depends on the charge passing through the tissue, which is the product of current and time. But how strongly the reactions occur at each pole also depends on how that current is distributed across the electrode area. If the current is high, more ions are pushed and the local pH change is stronger. If the same current is spread over a larger area, the current density is lower and the reaction is less intense; if it’s concentrated on a smaller area, the reaction is more intense. Therefore, both the overall current intensity and the current density at each pole determine the acid and alkaline reaction strengths.